1. Field of the Invention
This invention relates generally to electrical reactors and more specifically to iron core shunt reactors utilizing a liquid or gas coolant.
2. Description of the Prior Art
Power may be regarded as consisting of two components, real power measured in watts and reactive power measured in VAR's. The term VAR is derived from "volt-amperes reactive". For a transmission line the VAR requirements increase with the square of the voltage. The VAR requirements also increase with increased line capacitance and longer transmission lines. The use of long high voltage (HV) and extra high voltage (EHV) transmission lines, with high voltage defined as 100 kV to 229 kV, and extra high voltage defined as all voltages over 230 kV, has resulted in attendant increases in the VAR requirements on the systems connected to the end of the transmission lines. Further, the increased capacitance of bundled conductors commonly used for EHV transmission lines has greatly increased the VAR requirements compared with the conductors normally used with high voltage transmission lines.
The VAR requirements are important because if the system located at the end of the transmission line is unable to absorb the VAR's produced, the terminal voltages may rise to magnitudes capable of damaging apparatus connected thereto. Accordingly, it has become common to provide compensation for long HV and EHV transmission lines which may have periods of light loads, or transmission lines which are lightly loaded in the early stages of development of the system they are servicing. This compensation is provided by connecting shunt reactors to the HV or EHV line at the receiving end of the system. Shunt reactors may also be connected to the line at one or more selected intermediate points depending upon the length and the voltage profile desired across the transmission line.
There are two main types of shunt reactors, reactors having an air core and reactors having an iron core. An example of an air core reactor is U.S. Pat. No. 3,902,147. Disclosed therein is an air core duplex reactor consisting of two or more sets of rigid cylindrical coil assemblies disposed in concentric, radially spaced relation. Another example of an air core reactor is U.S. Pat. No. 3,621,427, which is assigned to the same assignee as the present invention. The reactor disclosed therein utilizes series connected pancake windings immersed in a liquid insulating and cooling dielectric such as mineral oil. This allows the reactor to be operated at higher voltages. It is noteworthy to point out that technically the reactor does not have on air core since the air has been displaced by the liquid coolant. However, since the reactor does not have a core capable of shaping the field of magnetic flux, the reactor is considered by the industry to be an air core reactor.
An example of an iron core reactor is U.S. Pat. No. 3,504,321 which is assigned to the same assignee as the present invention. Disclosed therein is a duplex reactor utilizing two long coils constructed of several turns of a sheet or foil conductor. Iron core reactors have also been used in conjunction with liquid insulating and cooling dielectrics thus allowing them to operate at higher voltages.